1. Field of the Invention
The present invention relates to a target device used for examining eye movement and more particularly to a target device for executing an ocular motion nystagmus (eye movement) test in which nystagmus is induced by a stripe pattern target.
2. Prior Art
One of the diagnostic methods used in the clinical examination of a patient's labyrinth, nerves balance or functional disorders of the central nervous system is measurement of eye movement.
Since eye movement tests can reveal symptoms of these problems, various eye movement testing devices are currently used. In these devices, eye movement is tested based upon a condition called "nystagmus" which is obtained when the examinee sees a stationary or movable target.
Of the various types of eye tests, the optical kinetic nystagmus ("OKN") test examines eye movement that is induced to prevent image lag caused by a lag signal generated by an image from the surrounding area formed on the retina when the examinee or the surrounding area around the examinee rotates. The OKN is induced at its maximum when the entire area surrounding the examinee rotates.
Whereas a "follow-the-target" type test tends to induce intentional eye movement with little reactionary eye movement, the OKN test allows for both intentional and reactionary eye movement and thus reveals symptoms of cerebral disease (of a one-sided and extensive disorder or of an acute nature) by measuring the difference between the OKN values of each eye.
The simplified qualitative "follow-the-target" test currently used is a so-called "Tape OKN" test. This test utilizes a tape which is about one meter long with a black-and-white stripe pattern. The tape is moved horizontally or vertically manually in front of the examinee's eyes and OKN induction is thus observed.
Another type of quantitative method used in general practice is one where an examinee enters a rotary drum which has stripe patterns on the inner surface. The drum is rotated electrically, and signals are taken from ENG (electrodes) attached to the top, bottom, left and right sides of the eyes so that the signals are collected, recorded and analyzed.
The above two methods have problems, however. In the Tape OKN test, the tape must be moved manually, and the test result is qualitative, not quantitative. In the second test method which uses the rotary drum, the equipment required is quite large in size, and thus, a large amount of space and manpower are necessary to operate it. Accordingly, this testing method is cumbersome and difficult to implement.